French/Aco Drain?

[jungle_jim01]

Hi, i've just spoken to a builder about resurfacing our driveway and solving our penetrating damp problem in the process. The issue we have is that the internal floor level is about 1ft below outside, (both of which are concrete). The builder has suggested digging out a trench outside to below internal floor level, lining the wall with some kind of membrane and installing Aco drainage. Does anyone have any experience/thoughts/info on this kind of installation?
Thanks for your help.

 

[MatthewC]

I've no experience of ACO but I would have thought (looking at their website) that a "normal" French drain would be cheaper. Lots of people here have done that without esorting to such expensive looking stuff, I think. You'll need to go down (if you can) six inches below the floor level.

Have you thought about where you will drain the water? Can you connect to an existing rainwater drain at the right level or will you have to dig a soakaway? That's the most important issue, I reckon.

 

[jungle_jim01]

Hi, thanks for the reply. I had thought about a land drain, piped into existing drainage. However, another builder has suggested the following:
"i would suggest we dig out along the wall and create a barrier between the wall and the aggregates using a medium dense breeze block then bed the channel on top."
I've no experience with this so really not sure. Any other thoughts really appreciated

 

[jungle_jim01]

So many different opinions...getting confused :?
I've also been using another building forum and a variety of responses suggesting that no matter i what i do below ground level the sandstone will still be damp. Am i missing something?...surely a well drained French drain, coupled with good surface drainage should drive moisture away from the walls?
I would have thought that either a membrane on the wall or breeze blocks in addition to the above would all help prevent the ingress of water.

Thanks again for your help.

 

[DJH]

I would be inclined to extend the damp proof membrane, if you can, to above ground level and if possible, bearing in mind we don't know the construction of your house, somehow terminate it behind a plinth perhaps to prevent moisture getting behind it and causing damp that way but certainly have it higher than finished ground level. If you are building a block wall as you describe I think you would get better results if the damp proof membrane is fitted in front of the blocks rather than sandwiched between them and the wall. The blocks should be built on a damp course also so to keep them as dry as poosible.

I would also use the dpc membrane under the stones for the french drain and bring it up a good way against the soil of the trench. This will in itself form a sort of gutter. I have used this method myself with good results so far. Its also good if when back filling that a permeable membrane is put between the stone filling and the soil side of the trench. This will hold back mud and debris and plant roots. Over the top I'm sure you may think but I've done all this with good results.

Doug

 

[stuart45]

I use the other forum quite a lot and know that you will probably get better advice on here with regard to dampness in older properties. I'm actually putting a French drain in for someone at the moment where the exterior ground level is about 2 ft higher than the inside floor. The water was coming up through the floor a few weeks ago in the heavy rain.

 

[DJH]

Which part of Somerset Stuart being a Somerset lad myself.
Doug

 

[stuart45]

I live in the Blackdown Hills, although we don't originate from these parts. Came here about 10 years ago from Sussex.

 

[DJH]

Know them well Stuart, used to skittle at the Lamb and Flag B st M years ago.

 

[Penners]

builder has suggested the following:
"i would suggest we dig out along the wall and create a barrier between the wall and the aggregates using a medium dense breeze block then bed the channel on top."

I vehemently disagree. Builders unused to period buildings will often recommend "solutions" that involve sealing the wall against externally penetrating damp. The trouble is that this technique also seals internal damp into the wall.

The important principles (in my amateur view) are these:

* Get the external soil level down below the internal floor level - the further below the better, so long as you don't dig down below the bottom of the plinth.

* Leave the exterior of the plinth as exposed as possible to air circulation.

* Ensure that surface water management provisions are effective and well maintained.

* Arrange for any water that may seep or fall into the excavation to be channelled away properly.

Obviously the methods used to achieve this will vary from building to building, depending on your particular conditions. But if the above principles are observed you should considerably ameliorate your damp problems.

 

[jungle_jim01]

Thanks Penners, that's what my gut instinct was. The difficulty that i have is that i can't lower the ground more than a couple of inches without creating a download slope towards the house. So i guess the next best thing is a well drained french drain, lined with a membrane and filled with large aggregate?

Something that's been playing on my mind...the area is currently concrete which must help (to some degree) stop water from penetrating the ground and walls...presumably water is drawn up from the ground? yet the problem i have with damp is definitely worse after rain.

Thanks again, any more advice really appreciated

 

[MatthewC]

Something that's been playing on my mind...the area is currently concrete which must help (to some degree) stop water from penetrating the ground and walls...presumably water is drawn up from the ground? yet the problem i have with damp is definitely worse after rain.

Do you mean that you have concrete up to the walls and it is this concrete which is above the floor level by a foot? This was the sort of thing that I had, and it is basically lethal to the house. Dampness always gets in through joins between the concrete and the house, and so water from the concreted area is always seeping into the wall and producing dampness inside. It's not "drawn up from the ground" but rather it seeps in where it can and then never gets out. This dampness is even worse if the wall and floor of your house are something porous like the Cotswold stone and quarry tiles on sand, like mine was!

I suggest that the first thing you do is to hire an angle grinder and cut the concrete back by about a foot or more, parallel to the walls. Then dig out the rubble and as much earth as you can, and leave it to dry out. This should prove pretty quickly that it is a major cause of your problems.

If your house is of old construction (exactly what is it?), that will allow the walls to breathe and, if you've gone down well below the floor level, the walls will dry out inside.

 

[jungle_jim01]

Hi, and thanks for the detailed reply. This part of the house is mostly victorian brick but the lower courses are Yorkshire sandstone so yes quite porous. I'd wondered about digging out but worried that unless i put proper drainage in at the same time i might just end up creating a ditch that will fill with water and make things worse? The soil is quite clayey i think.

 

[elizabeth]

Hi Jungle,

we will face the same dilemma ourselves soon on account of the neighbours soil banked up against our end of house wall by about 3ft. I understand what you mean by ensuring good drainage because you may not solve the problem unless the water has a natural incline to drain especially on clay soil - so I believe. Would it be possible to dig the ditch so any collecting water drains off at the end away from the house walls?

 

[Penners]

Something that's been playing on my mind...the area is currently concrete which must help (to some degree) stop water from penetrating the ground and walls

On the contrary, the concrete will stop ground moisture from evaporating off to atmosphere, trapping it in the soil. It's therefore likely to migrate sideways and saturate the walls. You'll also be getting rain-bounce splashing up against your walls.

The concrete floor inside will probably be having the same effect, but obviously - unless you're prepared to dig it all out - it's more difficult to do anything about that. But at least if you expose the plinth on the outside, you'll help the situation.

 

[jungle_jim01]

Thanks for all the help so far. Yeah don't fancy digging out the inside! But i think i'll try and dig a trench with a slight slope away from the wall before going ahead with drainage and surfacing. Hopefully have a chance to dry out a bit. Then i think i'll go with a French type drain to take water away...still deciding whether it's a good idea to go down the membrane route or not (http://www.sdg.ie/waterproofing/tanking-membranes/bitusheet/).
Someone else did suggest adding benonite up the sides of the wall but this is something else completely new to me and bit of a minefield!

 

[Keithj]

Been there, in spades. Avoid clever damp barrier materials - they don't work (I have photographs to show how pointless an injected damp course was in our house).

We had a concrete path all round the house, and damp problems aplenty.

We had the concrete removed and a French drain dug (all round) running the water off into the (piped) ditch that runs at the back of the property. The French drain is lined with some porous cloth (might be nylon or similar) and filled with largeish shingle. The damp problem is gone. It was a simple and very effective cure.

The church had a similar damp problem until recently - the soil outside is a foot or so higher than the inside. A French drain was dug a few months ago, and the walls are drying out well. The builder also found that part of the wall was hanging over a void where underground water had washed away the subsoil under it - he was bright enough to realise that while he should not dig below the foundations, what he'd found needed investigation.